Shoe roll

ABSTRACT

For profiling a fiber web (W) a shoe roll ( 10 ) defines a roll nip ( 4 ) with an opposite counter-roll ( 3 ). The shoe roll ( 10 ) has a static roll frame ( 5 ), a shoe element ( 2 ) located at the roll nip ( 4 ) and an endless belt ( 6 ) rotating about the shoe element ( 2 ) and the static roll frame ( 5 ). A lubricating cycle ( 71 ) is provided between the endless belt ( 6 ) and the shoe element ( 2 ) in the roll nip. The surface of the web (W) is profiled in the nip by loading the loading element ( 8 ). Before or after the shoe element ( 2 ), the shoe roll ( 10 ) has a longitudinally extending profiling strip ( 1 ) which can be pressurized to be able to perform thickness profiling of the surface of the fiber web (W). The static roll frame ( 5 ) and the shoe element ( 2 ) the endless belt ( 6 ) rotate about the profiling strip.

CROSS REFERENCES TO RELATED APPLICATIONS

This application is a national stage application of InternationalApplication No. PCT/FI02/00278, filed Feb. 4, 2002, and claims priorityon Finnish Application No. 20010678, Filed Apr. 2, 2001.

STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSOREDRESEARCH AND DEVELOPMENT

Not applicable.

BACKGROUND OF THE INVENTION

The invention relates to an arrangement for profiling a fibre web on ashoe roll.

In shoe calenders, the nip pressure is usually in the range from 2–15Mpa and the nip pressure is controlled by means of the tilt of the shoeelement combined with loading. A shoe calender has a relatively longshoe element in the machine direction, often of up to 270 mm or more,thus allowing good surface smoothness of the fibre web while preservingthe bulk, because despite the relatively high loading pressure of theshoe element, the maximum pressure in the roll nip will remainrelatively low.

However, especially in pre-calendering of the fibre web, surfacethickness profiling is often required in addition to surface smoothnessprofiling of the fibre web. Current shoe calenders are not suitable forsurface thickness profiling, because the maximum compression loadachieved in the roll nip with these is relatively low despite the highloading pressure of the shoe element. If a shoe calender is used forpre-calendering a fibre web such as a cardboard web, one has nowadays tocarry out thickness profiling of the fibre web surface with a separatehard profiling roll. A separate calender for thickness profilingincreases the machine direction space requirement regarding the shoecalender alone, and also increases the purchasing and operating costs ofthe paper and cardboard making machine. If a hard roll for surfacethickness profiling is brought into contact with the counter-roll of theshoe roll (thermo-roll), the machine direction space requirement willdecrease, but the operating and purchasing costs of the installation arestill higher than they would be, could a shoe calender alone be used forpre-calendering. In some cases, the fibre web feed may also causeproblems.

The arrangement of the invention and the shoe roll used in it areintended to overcome the shortcomings in the prior art.

SUMMARY OF THE INVENTION

Thus the main purpose of the invention is to achieve a shoe roll thatallows smoothness, glaze, humidity and thickness profiling of the fibreweb surface to be performed.

The invention is based on the fundamental idea that, underneath anendless belt rotating about the shoe roll, a narrow continuous profilingstrip is provided to extend substantially from one end to the other inthe longitudinal direction of the shoe roll. The profiling strip ispreferably located in the roll nip, in the immediate vicinity of theshoe of the shoe roll (also referred to as a shoe element below). Due tothe narrow profiling strip, the area of the roll nip between theprofiling strip and the counter roll will be small, and then thecompression load required for surface thickness profiling in the rollnip (nip pressure) can be provided at a sufficiently high level evenwith relatively low loading pressures of the profiling strip.

In the arrangement of the invention for profiling a fibre web, the shoeroll has an opposite counter-roll and the shoe roll and the counter-rollare separated by the roll nip, whereby

the shoe roll has a static roll frame, a shoe element at the roll nipand an endless belt rotating around the shoe element and the static rollframe,

a lubricating cycle is provided between the endless belt and the shoeelement,

as the fibre web is passing through the roll nip, its surface isprofiled by loading the shoe element with loading elements,

the shoe roll also comprises a profiling strip extending substantiallyfrom one end to the other of the roll in the longitudinal direction,

the profiling strip can be pressurised so as to be able to performthickness profiling of the fibre web surface, and

the endless belt rotates around the profiling strip in addition to thestatic roll frame of the shoe roll and the shoe element.

The profiling strip is preferably located in the roll nip, immediatelyafter the shoe element, with the roll nip viewed from the inputdirection of the fibre web.

The shoe roll of the invention has a fibre web profiling strip which isnarrow in the machine direction and which achieves the significantadvantage over known calendaring and press installations thatsmoothness, glaze and thickness profiling of the fibre web and humidityand thickness profiling in shoe presses can now be performed with onesingle shoe calendar. Using the shoe element of the shoe calender, it ispossible to achieve good surface smoothness of the fibre web whilepreserving the fibre web bulk. A profiling strip disposed in connectionwith the shoe of the shoe calender (shoe element), in turn, allowsefficient thickness profiling of the fibre web.

Using one single shoe calender for thickness and smoothness profiling ofthe fibre web achieves notable savings in service, purchasing andoperating costs compared to a situation, where thickness and smoothnessprofiling of the fibre web are performed by two separate calenders. Atthe same time, the machine direction space requirement is reduced, whichis a benefit when a calendering line is installed on confined sites.Compared to the situation where calendering is performed with a shoeroll and a hard chilled roll mounted in connection with the samethermo-roll (counter-roll), benefits are gained in the form of reducedoperating, service and purchasing costs. The fibre web feeding alsobecomes simpler when one single shoe calender is used for calenderinginstead of using a shoe roll and a hard profiling roll mounted inconnection with the same thermo-roll.

The shoe roll of the invention, which is equipped with a profilingstrip, can be used also in connection with presses for thicknessprofiling of a fibre web. Presses are used in paper and cardboard makingmachines for mechanical dewatering of the fibre web. Such presses have apress shoe fixed to a stationary frame, about which an endless beltrotates. Opposite the press shoe, a hard press roll is disposed. On oneor usually both sides of the fibre web, a water-absorbing press fabricis provided to absorb water in the roll nip between the press shoe andits opposite press roll. Between the press shoe and the belt, alubricating cycle is arranged in the roll nip in order to reduce thefriction between these. Humidity and thickness profiling of the fibreweb surface takes place between the press shoe and the press roll.

In such a press equipped with a shoe roll, the term shoe element impliesthe press shoe of the press. Accordingly, a roll frame implies thestatic press frame, to which the press shoe is attached.

In this application, the shoe element length and the roll nip lengthstand for the machine direction length of the shoe element and the rollnip, respectively. U.S. Pat. Nos. 5,645,691 and 4,741,905 disclose wetpresses equipped with shoe elements, comprising various supplementaryparts for enhancing dewatering action. However, these inventions do notallow the pre-calendering result of a fibre web, especially that of acardboard web, to be improved as does the arrangement of the inventionand the shoe roll used in this.

The invention is described more in detail below with reference to theaccompanying drawing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic cross-sectional view of a part of the shoe rollof the invention, viewed from the end of the pair of rolls between theshoe roll and its opposed counter-roll.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The shoe calender 9 shown in FIG. 1 has a shoe roll 10, having anopposite heated hard roll, i.e. thermo-roll 3. Regarding the shoeelement of the shoe roll and its loading and lubricating systems, theshoe calender 9 has a conventional design per se, and hence the figureshows only part of the shoe roll in order to illustrate the inventiveidea. The shoe roll 10 has a static frame 5, with only its upper partshown in the figure, a loading element 8 bearing against the staticframe 5 with its lower surface, and a shoe element 2 on top of theloading element. The first part 4 a of the roll nip 4 is located betweenthe shoe element 2 and the counter-roll 3. Adjacent to the shoe element2 of the shoe roll, there is a profiling strip 1, which in this case islocated after the first part 4; 4 a of the roll nip, with the roll nip 4viewed in the input direction of the fibre web W. The input direction ofthe fibre web has been indicated in the figure with an arrow with a fullhead.

The second part 4 b of the roll nip 4 is between the profiling strip 1and the counter-roll 3. An endless belt 6 slides in the roll nip 4; 4 a,4 b on the upper, i.e. slide surface 2 a of the shoe element 2 and onthe upper surface 1 a of the profiling strip 1. This endless beltrotates about the static frame 5 of the shoe roll, the shoe element 2and the profiling strip 1. A lubricating oil cycle 71 has been providedwith a lubricating system 7 in the roll nip 4, between the slide surface2; 2 a of the shoe element and the upper surface 1 a of the profilingstrip and the endless belt.

The slide surface 2 a of the shoe element forms a concave pocket whenthe roll nip 4; 4 a is viewed from the direction of the counter-roll 3.By contrast, the upper surface 1 a of the profiling strip has a concaveshape when the roll nip 4; 4 b is viewed from the direction of thecounter-roll 3, so that the nip pressure between the thermo-roll and theprofiling strip will rise sufficiently with a view to thicknessprofiling of the fibre web. The profiling strip 1 has a width parallelto the longitudinal axis of the shoe element, which is roughly the sameas the width of the shoe element. Thus the profiling strip extendssubstantially from one end to the other of the shoe roll in itslongitudinal direction.

The profiling strip 1 is substantially continuous and has a length inthe machine direction, which is significantly smaller than the length ofthe shoe element. With the roll nip 4 viewed from the directionindicated by the arrow with a full head, i.e. in the input direction ofthe fibre web W, the roll nip 4 first comprises a conventional roll nip4; 4 a between the shoe element 2 the shoe roll and the thermo-roll 3,followed by a roll nip 4; 4 b between the profiling strip 1 and thethermo-roll 3. Viewed from the direction of the counter-roll 3, the rollnip 4 first comprises a fibre web W and an endless belt 6 underneaththis. Underneath the endless belt rotating on the axial frame 5 of theshoe roll 10, in turn, the shoe element 2 and the profiling strip 1 aredisposed.

Different nip pressures are usually exerted on the first part 4 a andthe second part 4 b of the roll nip 4. The nip pressure is generated inthe first part 4 a of the roll nip 4 with rows of press cylinders 81; 81a; 81 b provided underneath the shoe element 2 and with which the shoeelement 2 is pressed (loaded) against the counter-roll 3. The rows ofpress cylinders 81 a and 81 b bear against the frame 5 at their lowerpart. The rows of press cylinders 81 a and 81 b may generate the same ordifferent compression loads on the front part 21 and the rear part 22 ofthe shoe element. The nip pressure of the second part 4; 4 b of the rollnip, again, is generated with a press cylinder 8; 82 provided underneaththe profiling strip, the press cylinder bearing on the frame 5 at itslower part. Although the profiling strip is loaded, i.e. pressed againstthe counter-roll by the pressure cylinder 8; 82 usually at lowerpressure than is the shoe element by the press cylinder 8; 81, the nippressure formed between the profiling strip and the counter-roll willbecome appreciably higher than the nip pressure formed between the shoeelement and the counter-roll, owing to the smaller area of the uppersurface 1 a of the profiling strip in the roll nip.

As the roll nip is closed by loading the shoe element of the shoe rolland/or profiling strip with loading elements 8; 81, 82, the fibre web W,such as a heated cardboard web, will be pressed in the two-part roll nip4; 4 a, 4 b between the heated counter-roll (thermo-roll) 3 and the shoeroll 10 and the profiling strip 1, while its surface is beingcalendered. As a specific part of the fibre web W enters the first part4 a of the roll nip between the shoe element and the counter-roll, thefibre web surface is smoothness profiled while the bulk level ispreserved at a high level. Smoothness profiling occurs owing to therelatively low nip pressure prevailing in the roll nip 4 a. The nippressure will remain low, even if the total loading pressure generatedwith the loading elements 8; 81 on the shoe element, i.e. the linearpressure, were relatively high, because the shoe element area isrelatively large (the shoe element may have a machine direction lengthof up to 270 mm or more). After this, the same fibre web W part reachesthe second part 4 b of the roll nip 4 between the thermo-roll and theprofiling strip. The compression load in the roll nip 4; 4 b now dependsmainly on two factors; the area of the upper surface of the profilingstrip and the loading pressure of the profiling strip. Since theprofiling strip 1 should have a width roughly equal to that of the shoeelement 2, the machine direction length of the upper surface 1 a of theprofiling strip should be dimensioned for a shoe calender of a givenwidth such that a given loading pressure of the profiling strip allows asufficiently high compression load (nip pressure) to be achieved betweenthe profiling strip and the counter-roll in the roll nip 4; 4 b. Theloading pressure of the profiling strip can be kept relatively low (5–15Mpa), while the nip pressure achieved in the second part 4; 4 b of theroll nip still rises to a high level. This is due to the fact that theprofiling strip 1 is considerably shorter in the machine direction thanthe shoe element 2, and in addition, it may have a convexly shaped uppersurface, so that the area of the upper surface 1 a of the profilingstrip 1 is but small in the roll nip. Owing to the high nip pressures,the surface of the fibre web is profiled as desired in the thicknessdirection of the fibre web.

The example above exemplifies only one embodiment of the shoe calender 9of the invention, and the inventive idea can be carried out in severalother ways as well, without departing from the scope of the inventiveidea defined in the claims. Usually the profiling strip is located inthe immediate vicinity of the shoe element in the roll nip. However, itis also conceivable to dispose the profiling strip elsewhere underneaththe endless belt rotating about the shoe roll. In one option, theprofiling strip is disposed on the opposite side of the shoe roll viewedfrom the roll nip, i.e. at a distance of 180 degrees from the roll nipin the cross-sectional circle of the shoe roll.

In some cases, the profiling strip 1 may be disposed before the shoeelement 2 when the roll nip is viewed from the input direction of thefibre web W.

In the example above, the shoe element of the shoe calender waspressurized by means of two rows of hydraulic cylinders. Both in shoecalenders and in shoe presses, however, the shoe element can bepressurized with e.g. one row of hydraulic cylinders or with any otherloading elements known in connection with shoe calenders and shoepresses.

1. A paper or cardboard making machine defining a machine direction,comprising: a shoe element defining a longitudinal axis extending in acrossmachine direction, the shoe element having a machine directionlength and a longitudinal direction length along the longitudinal axis,the shoe element mounted to a static frame by a plurality of firstloading elements; a profiling strip considerably narrower than the shoeelement in the machine direction, and roughly equal in longitudinaldirection length, and mounted to the static frame by a plurality ofsecond loading elements, the profiling strip located in the immediatevicinity of the shoe element spaced downstream in the machine directionfrom the shoe element; an endless belt rotatably mounted about the shoeelement, the profiling strip and the static frame; an opposedcounter-roll forming a first nip with the roll shoe and a second nipwith the profiling strip so that the endless belt passes through thefirst nip and the second nip; and a lubricating system arranged toproviding a lubricating cycle between the endless belt, and the shoeelement and the profiling strip.
 2. The paper or cardboard makingmachine of claim 1 wherein the first loading elements and the secondloading elements are of the same type.
 3. The paper or cardboard makingmachine of claim 1 wherein the profiling strip is substantiallycontinuous.
 4. The paper or cardboard making machine of claim 1 whereinthe profiling strip has a convexly shaped upper surface.
 5. The paper orcardboard making machine of claim 1 wherein the opposed counter-roll isa thermo-roll.
 6. The paper or cardboard making machine of claim 1wherein the second nip is arranged so the second nip has a higher nippressure than the first nip.
 7. The paper or cardboard making machine ofclaim 6 wherein the first nip pressure is arranged to be between 2 to 15Mpa.
 8. The paper or cardboard making machine of claim 1 wherein theopposed counter-roll is a thermo-roll.
 9. The paper or cardboard makingmachine of claim 1 wherein the shoe element has a machine directionlength of at least about 270 mm.
 10. A paper or cardboard making machinedefining a machine direction, comprising: a shoe element defining alongitudinal axis extending in a crossmachine direction, the shoeelement having a machine direction length and a longitudinal directionlength along the longitudinal axis, the shoe element mounted to a staticframe by a plurality of first loading elements; a profiling stripconsiderably narrower than the shoe element in the machine direction,and roughly equal in longitudinal direction length, and mounted to thestatic frame by a plurality of second loading elements, the profilingstrip located in the immediate vicinity of the shoe element spaceddownstream in the machine direction from the shoe element; an endlessbelt rotatably mounted about the shoe element, the profiling strip, andthe static frame; an opposed counter-roll forming a first nip with theroll shoe and a second nip with the profiling strip so that the endlessbelt passes through the first nip and the second nip; a lubricatingsystem arranged to provide a lubricating cycle between the endless belt,and the shoe element and the profiling strip; and wherein the first nipis loaded to a first nip pressure and the second nip is loaded to apressure greater than the first nip.
 11. The paper or cardboard makingmachine of claim 10 wherein the profiling strip has a convexly shapedupper surface.
 12. The paper or cardboard making machine of claim 10wherein the first loading elements and the second loading elements areof the same type.
 13. The paper or cardboard making machine of claim 10wherein the first nip pressure is between 2 to 15 Mpa.
 14. The paper orcardboard making machine of claim 10 wherein the profiling strip issubstantially continuous.
 15. The paper or cardboard making machine ofclaim 10 wherein the first nip and the second nip are arranged forsmoothness and thickness profiling of the fibre web respectively. 16.The paper or cardboard making machine of claim 10 wherein the second nipis arranged so the second nip has a higher nip pressure than the firstnip.
 17. The paper or cardboard making machine of claim 10 wherein theshoe element has a machine direction length of at least about 270 mm.18. A paper or cardboard making machine defining a machine direction,comprising: a shoe element defining a longitudinal axis extending in acrossmachine direction, the shoe element having a machine directionlength and a longitudinal direction length along the longitudinal axis,the shoe element mounted to a static frame by a plurality of upstreampress cylinders, and a plurality of downstream press cylinders spaceddownstream from the upstream press cylinders in the machine direction; aprofiling strip considerably narrower than the shoe element in themachine direction, and roughly equal in longitudinal direction length,and mounted to the static frame by a further plurality of presscylinders, the profiling strip located in the immediate vicinity of theshoe element and spaced downstream in the machine direction from theshoe element; an endless belt rotatably mounted about the shoe element,the profiling strip and the static frame; an opposed counter-rollforming a first nip with the roll shoe and a second nip with theprofiling strip so that the endless belt passes through the first nipand the second nip; and a lubricating system arranged to providing alubricating cycle between the endless belt, and the shoe element and theprofiling strip.
 19. The paper or cardboard making machine of claim 18wherein the upstream press cylinders, the downstream press cylinders andthe further plurality of press cylinders are of the same type.
 20. Thepaper or cardboard making machine of claim 18 wherein the profilingstrip has a convexly shaped upper surface.
 21. The paper or cardboardmaking machine of claim 18 wherein the shoe element has a machinedirection length of at least about 270 mm.